1. Field of the Invention
The present invention relates to a substrate for ink jet head for use in an ink jet head for discharging an ink and recording images of characters or the like with the ink discharged. The present invention relates also to an ink jet head in which said substrate for ink jet head is used. The present invention further relates to an ink jet apparatus provided with said ink jet head. The present invention includes a process for producing said substrate for ink jet head.
2. Background of the Invention
As for the ink jet recording system, there have been proposed a variety of systems. Among such proposals, as a typical one, the public attention has been focused on those ink jet systems disclosed, for example, in U.S. Pat. Nos. 4,723,129 and 4,740,796 in recent years. These ink jet systems are of the type that an ink is discharged utilizing thermal energy and recording is performed with the ink discharged. And there are advantages for these ink jet systems that recording of a high quality image with a high density and a high resolution can be performed at a high speed, and it is relatively easy to make a head or an apparatus compact.
By the way, the typical configuration of a so-called substrate (hereinafter occasionally referred to as "head substrate") which constitutes the head used in such ink jet system as above described is, for example, such that is schematically shown in FIG. 3. In FIG. 3. FIG. 3(a) is a schematic plan view and FIG. 3(b) is a schematic cross-sectional view taken along line D-D' in FIG. 3(a).
The head substrate of the configuration shown in FIG. 3 is generally produced through steps shown in FIG. 1 and FIG. 2. In FIG. 1, FIG. 1(a) is a schematic plan view and FIG. 1(b) is a schematic cross-sectional view of FIG. 1(a). In FIG. 2, FIG. 2(a) is a schematic plan view and FIG. 2(b) is a schematic cross-sectional view taken along line D-D' in FIG. 2(a).
Explanation is to be made about the steps of producing the head substrate with reference to FIGS. 1 through 3.
As shown in FIG. 1(a) and FIG. 1(b), a material layer (two-layered layer) for forming a first electrode contact layer 2 comprising a heat-generating resistor layer composed of, for example, HfB.sub.2 and a layer composed of, for example, Ti being stacked in this order from the side of an insulating base member 1 and a material layer for forming a wiring electrode 3 composed of, for example, a good conductive material such as Al are formed on the insulating base member 1 by a thin film-forming technique such as an evaporation method, a sputtering method and a CVD method. Then, as shown in FIG. 2(a) and FIG. 2(b), the previously formed material layer for the electrode contact layer 2 and the previously formed material layer for the wiring electrode layer 3 are subjected to patterning by photolithography. Successively, as shown in FIG. 3(a) and FIG. 3(b), the patterned material layer for the wiring electrode layer 3 is subjected to further patterning to expose part of the electrode contact layer 2, thereby forming a heat generating portion 10. It is possible for the heat generating portion 10 thus formed to be used such that it is in contact with ink as it is, depending upon the kind of a material to constitute it. However, in general, in order to protect the heat generating portion from corrosion and the like by ink, a protective layer is formed thereon.
The head substrate is produced through these production steps. And an ink jet apparatus provided with an ink jet head having a plurality of discharge outlets capable of discharging ink in which the above head substrate being used has been commercialized.
However, for the ink jet apparatus, there is a demand for further improving not only its recording speed but also the quality of an image recorded. As an ideal ink jet head which can satisfy this demand, there can be mentioned such an ink jet head that is basically provided with numerous ink discharging outlets as many as possible such that they are arranged with a high density.
In order to realize such ideal ink jet head, such matters as will be mentioned in the following, which have been disregarded until now, will be spotlighted as the problems to be solved. That is, with respect to the head substrate, defects such as pinholes or missing portions occasionally occur at photoresist layer to be used, for example, at the time of performing patterning of wiring electrode and those defects occurred extend to the wiring electrode layer to be patterned, or film defects such as pinholes or the like occasionally occur at an electrothermal converting body during the film formation. These things eventually greatly influence on the yield in the case of producing a head substrate provided with numerous ink discharging outlets being arranged at a high density.
As a typical example of the situation as above described, there can be illustrated such a disconnection of tile wiring electrode as indicated by the mark C in FIG. 2 and FIG. 3.
In the case of a head substrate provided with a relatively small number of ink discharging outlets being arranged at a relatively low density, the above point can be more or less admitted even if the yield is relatively low. But it becomes a problem which cannot be disregarded in the case of a head substrate provided with numerous ink discharging outlets being arranged at a high density. Particularly, it is a serious technical subject. In the case of a so-called full-line type ink jet head which is provided with numerous ink discharging outlets being arranged at a high density along the entire width of the recording area of a member on which an image is to be recorded in which numerous electrothermal converting bodies are arranged at high density on a base member such that they correspond to said numerous ink discharging outlets.